Ka波段电磁波束调控表面特性研究

发布时间：2018-08-06 20:48

【摘要】：毫米波成像技术广泛应用于安检、医疗中,但目前,毫米波成像系统中聚焦部分无论是采用反射面天线或者透镜,体积庞大、笨重。设计一种结构紧凑、易于集成、体积足够小的聚焦方式对于加快毫米波成像技术向便携化发展具有重要意义。利用超表面进行波束调控为我们提供了新的思路。本课题主要研究35 GHz垂直入射情况下透射波束的偏转与聚焦。首先,我们设计了一种工作在35 GHz、主极化传播模式下,透射系数模值较大,透射相位随尺寸变化可以实现 π~+π相位覆盖的三层圆环单元结构用以构造偏转与聚焦表面。通过对不同尺寸内径单元进行大角度入射情况下S参数稳定性仿真分析,我们发现,在0~60°入射时,该圆环结构透射系数模值与相位基本保持不变,保证了偏转和聚焦表面边缘电磁波束的有效工作。根据推广的斯涅耳定律,我们进行了波束偏转表面的设计与仿真。我们分别设计了垂直入射条件下透射波束小角度21°与大角度72°偏转。CST仿真结果显示,透射波束有效偏转,与理论设计拟合良好,透射效率分别为86%与83%,能量得到有效传输。最后,我们进行了聚焦表面的设计。根据准光路定理,我们设计了聚焦于3λ0,5λ0和10λ0的聚焦表面。通过仿真结果的对比,我们发现在保持聚焦平面尺寸不变的情况下,焦距越短,焦斑越小,焦深越小,聚焦效果越明显。为方便测试,我们选择加工聚焦于5λ0的表面进行实物测试。仿真结果显示,此时,焦点附近电场由51.34 d BV/m增加到61.98 d BV/m,增加了10.64 d B。焦斑大小为8.4 mm,小于λ0。我们将焦点处场强与35 GHz时焦点处场强相差3 d B,且焦斑宽度小于λ0的频率范围,定义为聚焦表面的工作带宽。仿真结果显示该聚焦表面工作带宽为33~37 GHz,绝对带宽为4 GHz,相对带宽11.43%。实测结果与仿真结果良好拟合,该结构具有很好的聚焦功能。
[Abstract]:Millimeter wave imaging technology is widely used in security inspection and medical treatment, but at present, the focusing part of millimeter wave imaging system is bulky and bulky, whether it is a reflector antenna or a lens. It is of great significance to design a compact, easy to integrate and small enough focusing mode for speeding up the development of millimeter wave imaging technology towards portability. The use of the supersurface for beam control provides us with a new way of thinking. In this paper, the deflection and focusing of transmission beam at 35 GHz vertical incidence are studied. First of all, we design a three-layer ring element structure which works at 35 GHz, the transmission coefficient mode is large, and the transmission phase can cover the 蟺 ~ 蟺 phase with the change of the size to construct the deflecting and focusing surfaces. Based on the simulation analysis of the S-parameter stability of different size inner diameter elements under the condition of large angle incidence, we find that the transmission coefficient modulus and phase of the ring structure remain basically unchanged at 0 ~ 60 掳incidence. The effective operation of the electromagnetic beam at the edge of the deflection and focusing surface is ensured. According to the generalized Sneel's law, we design and simulate the beam deflection surface. The simulation results show that the effective deflection of the transmission beam is well fitted to the theoretical design. The transmission efficiency is 86% and 83%, respectively, and the energy is transmitted effectively. Finally, we design the focused surface. According to the quasi-optical path theorem, we design the focusing surfaces focused on 3 位 0 5 位 0 and 10 位 0. By comparing the simulation results, we find that the shorter the focal length, the smaller the focal spot, the smaller the focal depth, and the more obvious the focus effect is. In order to facilitate the test, we choose to process the surface focused on 5 位 0 for physical testing. The simulation results show that the electric field near the focal point increases from 51.34 d BV/m to 61.98 dBV / m, with an increase of 10.64 dB / m. The focal spot size is 8.4 mm, less than 位 0. The frequency range of focal spot width less than 位 0 is defined as the working bandwidth of the focusing surface, which is 3 dB different from that at 35 GHz and the focal spot width is less than 位 0. The simulation results show that the working bandwidth of the focused surface is 3337 GHz, the absolute bandwidth is 4 GHz, and the relative bandwidth is 11.43 GHz. The measured results fit well with the simulation results, and the structure has a good focusing function.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN015;TN820

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